The field of art to which this invention pertains is glycidyl ethers of polyhydric phenols and polyhydric alcohols.
Glycidyl ethers of polyhydric alcohols and polyhydric phenols are generally prepared by reacting the alcohol or phenol with epichlorohydrin to form a chlorohydrin ether which is then dehydrohalogenated to form the glycidyl ether. ##STR1## Incomplete dehydrohalogenation of the chlorohydrin ether group results in residual chlorine in the product, said residual chlorine being referred to as hydrolyzable chlorine or active chlorine. This residual hydrolyzable chlorine, even in amounts as low as 0.1 weight percent or less, can be detrimental to the properties, particularly, electrical properties, of the cured resins in many applications.
A process for manufacturing glycidyl ethers of polyhydric phenols is described in U.S. Pat. No. 2,801,227. A polyhydric phenol is dissolved in excess epichlorohydrin, the resulting solution is heated to about 100.degree. C. and aqueous caustic is then added. During the addition, epichlorohydrin and water are distilled over, the water is separated from the distillate and the epichlorohydrin is returned to the reactor. At the end of the reaction, the epichlorohydrin is removed by distillation, the resin is dissolved in a hydrocarbon solvent and the salt formed in the reaction is removed by filtration. The solvent is then removed by distillation. The glycidyl ether products have hydrolyzable chlorine contents of at least about 0.25%.
U.S. Pat. No. 3,309,384 describes a process for preparing glycidyl ethers of polyhydric phenols similar to that described in U.S. Pat. No. 2,801,227. However, after the dehydrohalogenation reaction and removal of epichlorohydrin, the resinous product is dissolved in methylisobutyl ketone and water is added to dissolve and wash out the salt. After separation of the water and salt, sodium hydroxide is added for a second dehydrohalogenation reaction. After washing, neutralization and removal of the solvent, the resulting glycidyl ethers are found to have hydrolyzable chlorine contents of less than 0.1 weight percent.
In U.S. Pat. No. 3,417,050, a manufacturing process for reacting a solution of epichlorohydrin and polyhydric phenol with finely divided caustic dispersed in a hydrocarbon is described. Glycidyl ethers having hydrolyzable chlorine contents as low as 0.07 weight percent are produced.
In Canadian Pat. No. 513,388, a process for preparing glycidyl ethers of polyhydric alcohols is described. Chlorohydrin ethers of the polyhydric alcohols are prepared by reacting the polyhydric alcohol with epichlorohydrin using boron trifluoride catalysts. The chlorohydrin ether so formed is dissolved in acetone and dehydrohalogenated with caustic. The resulting glycidyl ethers have hydrolyzable chlorine contents of less than 0.5%.
U.S. Pat. No. 4,447,598 is specifically directed to a process for reducing the hydrolyzable chlorine of glycidyl ethers to less than 300 ppm by dissolving the hydrolyzable chlorine containing glycidyl ether in a solvent mixture of toluene and methylethyl ketone followed by reaction with aqueous caustic.
In Japanese Patent Application No. 58-24578, the hydrolyzable chlorine content of glycidyl ethers of polyhydric phenols is reduced below 0.1 weight percent by conducting a second dehydrohalogenation of the glycidyl ethers in a polyoxyalkylene glycol or a crown ether solvent with alkali metal hydroxide.
British Patent Application No. 2,120,659A describes a process for preparing low hydrolyzable chlorine containing glycidyl ethers of polyhydric phenols which process involves dissolving the polyhydric phenol in a molar excess of epichlorohydrin plus a cyclic or linear ether, e.g., dioxane or diethoxyethane, followed by reaction with an alkali metal hydroxide.